This invention relates to vehicular propulsion systems and more particularly to such systems which utilize an electric motor drive.
The increasing awareness and concern regarding diminishing supplies of petroleum-based fuel, its rising costs and the pollutants and contaminants generated by internal combustion engines have heightened and emphasized the need for vehicular propulsion systems which do not require petroleum-based fuel nor cause pollution. Electrical motor driven vehicles powered by batteries would seem to meet these needs. Vehicles of this type have been known and used for many years but have enjoyed only limited acceptance and then only for relatively specialized uses. These vehicles, typically powered by secondary batteries, such as the conventional lead-acid battery, have not achieved success for a number of reasons. The relatively low energy density, both as to weight and volumetric aspects, the cost factors, the time and facilities needed to effect recharging and the limited cruising range have made wide-spread utilization of secondary batteries as a vehicular power source impractical for general use.
Other electrical power sources having increased energy density and perhaps some cost advantages over lead-acid batteries are zinc-air cell batteries and liquid electrode sodium-sulfur batteries. The former, as proposed, would be rechargeable with the zinc oxide produced during the discharge reaction being reduced and redeposited on the electrode during the recharging process. This recharging is time-consuming. Moreover, the filters and accessory equipment necessary to effect a rechargeable system poses substantial practical problems in adapting these batteries to wide-spread vehicular use. The liquid electrode type also has a markedly higher energy density, but the battery operating temperature is 250.degree. - 300.degree. C. and presents substantial problems in start-up from ambient temperatures.
Mechanically rechargeable batteries, i.e., those which are recharged by replacing an electrode consumed during the discharge reaction, and fuel cells are also known as electrical power sources but have not been adopted for general vehicular use for various reasons, including weight, costs and, in the case of fuel cells, the need to carry on board a supply of fuel, typically hydrogen.
U.S. Pat. No. 2,925,455 describes a continuous feed two-stage primary battery system in which the first stage generates hydrogen utilized by the second stage. However, the weight, cost and complexity of such a two-stage power supply with drive arrangements for continually feeding magnesium anode material to the first stage makes such a system impractical for mobile or vehicular use. Moreover, the cells of the first and second stage batteries are serially connected to provide power to the load, thus further increasing the complexity and difficulties in employing such a system for any mobile use.
Accordingly, the need continues for a practical vehicular propulsion system utilizing an on-board electrical power supply.